This invention relates in general to a word pronunciation voice verifying system for automatically verifying a plurality of words uttered by a speaker, and particularly to such a system for extracting the most recognizable characteristic feature from the voice.
The characteristic feature or parameter which has heretofore been employed in such a voice verifying system is extracted by a logic circuit based on the following formula: ##EQU1## WHERE, WHEN ##EQU2##
In the formula given above, x.sub.i is a characteristic parameter corresponding to a specified vocal sound x.sub.i ; F.sub.j is the output of a band pass filter for extracting a desired voice frequency; .gamma..sub.i is a threshold value; .alpha..sub.j, .beta..sub.j are weights added to the band pass filter. The component .SIGMA..beta..sub.j F.sub.j characterizes vocal sounds which are liable to be confused with a vocal sound x.sub.i and produce an error, and such component is therefore subtracted from the component .SIGMA..alpha..sub.j F.sub.j characterizing the vocal sound x.sub.i. If the value thus obtained is larger than a predetermined threshold value .gamma..sub.i, it is used as a characteristic parameter which characterizes the vocal sound x.sub.i so that a high verification accuracy can be obtained. The characteristic parameter extracted by formulas (1) and (2) can provide a highly stable verification for a specified individual for whom the weights .alpha..sub.j, .beta..sub.j and the threshold value .gamma..sub.i are previously set, but lacks stability when the speaker is replaced by another person. Thus, the prior art system is not suitable for the verification of a number of different speakers.